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Greenhouse Temperature Fluctuations

Discussion in 'Growing Areas' started by RadioFreeKirkwood, Feb 25, 2014.

  1. Feb 25, 2014 #1
    RadioFreeKirkwood

    RadioFreeKirkwood chloroplast envy Supporting Member

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    I recently constructed a 10'x14' greenhouse and have been monitoring temperature and humidity levels prior to moving all my plants into the new digs.

    I have a heater tied to a thermostat and feel pretty good about my temperatures not dipping too low.
    The greenhouse gets a good amount of sun and during peak time it warms up rather quickly. When it gets warm, vents open and it prevents the highs from being too high.

    My concern is that between when the greenhouse gets peak afternoon sun and when the sun goes down the temperature may change 15-20 degrees Fahrenheit in the span of 60-120 minutes.

    My questions are:

    a: how fast is too fast for temperature changes?
    b: am i better off lowering my peak temperatures to avoid significant temperature changes?
     
  2. Feb 26, 2014 #2
    KellyW

    KellyW Orchid wonk Staff Member Supporting Member

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    I have never heard anything about a rapid temperature change being a problem. I get temp changes as drastic or more and have never noticed a problem. Once you get the plants in there it will likely slow the temperature change somewhat and also buffer rapid humidity changes.

    Do you have a cooling system other than vents?
     
  3. Feb 26, 2014 #3
    Rvorchids

    Rvorchids Eric Sauer, Dayton Ohio

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    Programmable thermostats work well with say 4 settings a day can help moderate or lengthen the temperature differences. I also find that using this allows me to bring temps up over say 3-4 hours and the same for the evening drop. Much more like what would happen in the wild. The challenge is to work with the cooling control so that they don't fight it out. Early on in my greenhouse I went out to find the exhaust fan running with the heater trying to keep up.



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  4. Feb 26, 2014 #4
    RadioFreeKirkwood

    RadioFreeKirkwood chloroplast envy Supporting Member

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    Thanks both!

    Kelly, I am happy to know that you don't experience any ill effects with your plants in similar temperature shifts. I may be worrying over nothing. When I graph temperature and time, I just see these really fast spikes and assume it's bad.

    I have just placed a 150 gallon livestock water trough in the greenhouse in hopes of seeing some temperature and humidity regulation (and if a few aquatic plants happen to find there way in there, that's okay too).

    I don't currently have a cooling system apart from box fans and vents. I haven't had a hot day yet to know how hot it will get in there. I'm looking at a swamp cooler for the summer, but am open to creative (and thrifty) solutions. Most of my orchids are on the warm growing side of the spectrum, and I'd really like to avoid active cooling as much as possible. I also want to avoid a situation in early autumn, when hot days and cool nights might require active cooling during the day and active heating during the nights - the unfortunate heating vs. cooling grudge-match that Rvorchids describes sounds wasteful and expensive - and something I can see myself not catching on to if it happens when I'm not paying attention.
     
  5. Feb 26, 2014 #5
    KellyW

    KellyW Orchid wonk Staff Member Supporting Member

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    In a "normal" year I have periods in the spring and fall when I heat at night and cool during the day. However, this winter has been that way, too.

    I would be surprised if you can avoid some type of cooling system. When the outside air is hot and the sun is bright fans alone won't be enough, at least with my experience in my conditions. I know there are others on the Forum from the south so maybe they can give you some ideas. Good luck and enjoy that new greenhouse.
     
  6. Feb 27, 2014 #6
    Ray

    Ray Orchid Iconoclast Supporting Member

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    RFK - My greenhouse setup is similar to yours - heat maintained at a minimum temp, auto vents when the temp rises, 24/7 fans on the interior - plus I have a very large exhaust fan for when it gets REALLY hot.

    If you set the automatic vents to open somewhat cooler - mine are the "wax motor" type, that start activating at 65°F and are fully open at 75° - it "dampens" the rapid heating rate. (I cover the vents and disconnect the controllers in the winter. Don't need to be letting the very expensive heat out! It was 5° this morning.)

    I don't think the use of a programmable thermostat in the greenhouse is necessarily a great idea. I see a lot of folks want to boost the temperature in the daytime, and drop it at night. I suggest that letting the solar flux handle that is a much preferred way: If you let the sun warm the greenhouse, the photons hitting the plant increase commensurate with the temperature, which speeds up the plants' metabolism. If you artificially warm the plants, and it happens to be a cloudy day, the metabolism still increases, but the light input is insufficient, and that will lead to weak, leggy plants. (If you have supplemental lighting in the greenhouse, this argument "holds no water".)